Internal Bridging

Bandwidth Manager can forward traffic between two or more network cards. This feature is useful when the PC running the bandwidth manager acts as a bridge between two networks, or between a network and an ISP connection. Moreover, a bridge can be plugged into almost any network to manage and control its network flow. In other words, it works as a transparent bridge.

Bandwidth Manager Bridge

To define a bridge, select Tools - Bridging from the main menu and choose the Ethernet adapters you want to join:

Add/Edit Bridge window

Once a bridge is defined, the software begins forwarding the traffic between the bridged adapters and you can proceed with rules. It is not recommended to configure rules with the Any interface scope as that might cause double packet processing and lower the performance.

Since the bridge is transparent, your network addressing scheme does not change. For example, you put the bridge between your network that uses 192.168.0.x addressing and a router that has address Network cards merged into the bridge should be assigned any unused addresses in the 192.168.0.x range, so that the bridge itself will be able to communicate. The default gateway for network clients would still be because requests from the clients would come through the bridge transparently to the router and back.

Potential connectivity issues

In some cases, after you have enabled bridging you can find that although the computers in the LAN can access the Internet normally, the bridge itself is unable to access the Internet or to connect to any computer in the LAN. This happens because of an incorrect IP configuration and routing of the bridge. In the following example we use a 192.168.0.x network with a router assigned to explain the problem and suggest a solution:

Bridge example

A common mistake is to specify the default gateway on both NICs in the bridge. The following configuration is wrong because both NIC1 and NIC2 are assigned the default gateway while the gateway is hooked up to NIC1.

IP address:

IP address:

Essentially Windows does not know which NIC to use for Internet access, so it may be unable to establish the Internet connection. Simply remove the default gateway from all the NICs except the one connected to the router.

However, the bridge may still be unable to access the Internet and/or the LAN when both NICs are assigned IP addresses belonging to the same subnet. As the bridge has got two NICs assigned and, this is basically a routing issue. Suppose you want the bridge to connect to The question is which NIC should Windows choose to reach this address if it does not know which side it is hooked up to? Thereby we need to give Windows a hint using the route command and adjust the metrics.

Go to each NIC’s Advanced TCP/IP Settings and assign a metric manually. The metric is merely a number representing the cost of a route. We need to assign a higher metric to NIC1. For example, you can assign 100 to NIC1 and 50 to NIC2:

Advanced TCP/IP Settings

This will make Windows think the route through NIC2 is “cheaper” and it will route local traffic via this NIC properly. However, this will also break the Internet connection. In order to fix it, you need to execute the following command at a command prompt:

route -p add mask

This tells Windows: access via the NIC assigned So in this case Windows will access the Internet through gateway via NIC1 due to this explicit routing record, and all remaining local addresses via NIC2.